Metal surface such as aluminum



Aug. 20, 193 H. EDER ETAL 3,101,277 METHOD OF RENDERING METALLICSURFACES CORROSION RESISTANT Filed April 27, 1959 METAL SURFACE sucn ASALUMINUM 1 METAL SURFACE DEGREASED AND CLEANED OPTIONAL COATED WlT|-|LIQUID FUNCTIONAL MONOORGANOSILICON MATERIAL COATING AIR-DRIED r 1SURFACE RECOATED AND AIR-DRIED I OPTIONAL TREATED METAL HEATED TO ATLEAST 350C F' '"l 1 I TREATED METAL FURTHER COATED WITH A oPnoML PAINTOR VARNlSl-I A T TORNE' Y United States Patent 3,101,277 METHOD OFRENDERING METALLIC SURFACES CORROSION RESISTANT Heinz Eder, Gauting,near Munich, and Siegfried Bloeclt, Furth, Bavaria, Germany, assign'orsto Wacker-Chemie G.m.b.H., Munich, Bavaria, Germany Filed Apr. 27, 1959,Ser. No. 808,899 Claims priority, application Germany Apr. 30, 1958 9Claims. (Cl, 117-132),

This invention relates to a method of imparting corrosion resistance tometallic surfaces by treating the surface with an organosiliconcompound.

The flow diagram shown in the drawing illustrates the process of coatinga metal surface with a monoorganosilicone material.

The problem of the corrosion of metal surfaces resulting from oxidation,acid attack and alkali attack of the surface has plagued producer andconsumer alike. The use of protective coatings such as paints, lacquers,varnishes and the like has been a partial answer to this problem, butsuch materials are of limited effectiveness at high and low temperaturesand against acid or alkali attack. Furthermore the mechanical integrityof such cured films is not satisfactory in that the film breaks undermechanical stresses such as bending, pulling and striking the metal andthe cured films have not had satisfactory resistance to solvents andchemical agents in general.

In some cases, carefully produced oxide films are employed to protectaluminum, copper, magnesium and other metals from further corrosion.However the metallic surface must be substantially free of grease andother foreign matter or the metal must be pretreated prior to thesurface oxidation to achieve a satisfactory degree of protection.

It is an object of this invention to introduce a simple, economicalmethod of imparting corrosion resistance to metal surfaces. Anotherobject is to produce acid resistant and alkali resistant sheets, foilsand other forms of aluminum, copper, nickel and magnesium. Other objectsand advantages are apparent or will be detailed in the disclosure andclaims which follow.

This invention is a method of rendering metal surfaces corrosionresistant by coating the metal with a functional monoorganosiliconcompound and thereafter heating the coated metal to a temperature belowits melting point to cure the organosilicon composition.

The organosilicon compounds which are operable in this invention includesilanes and siloxanes. The operable organosilicon compounds have anorganic substituent to silicon ratio of from .9/1 to 1.2/1 andpreferably about 1/1. The balance of the .substituents attached tosilicon in these compounds are selected from oxygen atoms, hydroxyradicals and'alkoxy radicals. The operable silanes would be of thegeneral formula where each R is a monovalent hydrocarbon radical free ofaliphatic unsaturation or halogenatedv monovalent hydrocarbon radicalfree of aliphatic unsaturation, each R is hydrogen or alkyl, m has anaverage value of 0 to 1 inclusive, and n has an average value of .9 t0.1.2 inclusive, preferably about 1.0. The organic radicals representedby R include alkyl radicals such as methyl, ethyl, butyl and octadecyl,aryl radicals such as phenyl and anthracyl, alkaryl radicals such astolyl and methylnaphthyl, aralkyl radicals such as benzyl andphenylethyl, and cycloaliphatic such as cyclohexyl and cyclobutyl. Thepreferred and most common silanes are methy1-, phenyl-, andethyl-silanes.

The silanes can contain hydrogen substituents. There can be up to 1hydrogen atom per silicon atom in such 3 ,101,277 Patented Aug. 20, 1963lCe hydroxy and alkoxy radicals are present on the silanes.

wherein each R is an alkyl radical. Specific examples of operablesilanes include methyltriethoxy silane, methyltributoxy silane,methyldiethoxy silane, methyltrihydroxy silane, methylhydroxydiethoxysilane, methyldihydroxy silane, phenyltrimethoxy silane, ethyltriethoxysilane, tolyldiethoxy silane, benzyldihydroxy silane, andcyclohexyltrimethoxy silane. It is apparent that R can be the same ordifferent in each operable silane. The silane employed can be a singlespecie or it can be mixtures of silanes. Limited amounts ofdiorganosilanes and SiO units can be tolerated in the mixture, but thecloser the silane approximates an R/ Si ratio of about 1, the better theresults achieved.

The organosilicon compounds employed can be siloxanes. The operablesiloxanes are polymeric materials obtained by partial hydrolysis andcondensation or by complete hydrolysis and partial condensation or bypartial hydrolysis and partial condensation of silanes. I The silanesdescribed above can be employed as starting materials in the productionof the operable siloxanes. The silanes R I-l Si(OR') as defined abovecan be partiallyv hydrolyzed by conventional techniques to producesilanols such as R l-l SKOR) (OH) These silanols can then be condensedto siloxanes such as an m (OR, 4nmx x/ 2 and n m K 4-n-m-y( x-y y/ZAnother method involved complete hydrolysis of the silane to producesiloxanes of the unit formula and the partial condensate R H Si(OH) OAlcoholysis of the chlorosilanes produces alkoxy silanes from which theoperable siloxanes can be prepared as noted above.

The organosilicon compounds employed are liquids soluble in organicsolvents. They are usually relatively low molecular weight materialshaving viscosities of 1 to 10,000 cs. at 25 C. but they can be highviscosity materials of 1,000,000 cs. or more at 25 C.

The organosilicon compound is applied to the metal surface from asolvent solution, from an aqueous disper sion in an organic solvent, orfrom an emulsion. The solvent employed can be any organic solvent inwhich the particular organosilicon compound is soluble. Commonlyemployed as solvents are xylene, benzene, isopropyl, alcohol, aceticacid ethyl ester, Stoddard solvent, neutral minerals spirits, naphthasand other petroleum v solvents, and so forth.

The metal is coated by any desired means. Such varied coatingmethodsasbrushing, spraying, dipping, flowing, and so forth are operable. It isdesirable to form an unbroken film on the metal surface to secure evenprotection for the entire surface of the metal piece.

The metals can be in the fonm of sheets, bricks or pigs, foils or evencompleted parts such as gears, fenders for automobiles, flexible tubesfor use as ducts, packing cases arena 7 Q.) and the like. While thisinvention is applicable to metals generally, it is of particularimportance and usefulness with aluminum, nickel, copper, and magnesiumas well as with alloys containing such rnetals.

The metal is coated as described above and is subsequently heated to atemperature of at least 350 C. but below the melting point of the metal.This heating step imparts a permanence and additional resistance toalkali and acid to the protective coating. It is often desirable toallow some or all of the solvent to evaporate from the coating filmprior to heating. Thus the metal may be dipped in a tank containing asolution of organosilicon compound in an organic solvent, removed andairdried, then redipped if desired and again air-dried, then heated toabove 350 C. The resultant coating is clear and hard. The coating canonly be removed by extreme measures such as sandblasting or otherabrasion means removing a surface layer from the metal itself.

The coated metal can be used without further treatment or it can becoated with lacquers, enamels, and so forth.

Aluminum tubes employed for packaging shaving cream were coated bydipping in a 10% by weight solution of methyltriethoxy silane in xylene.The xylene was allowed to evaporate ofi the metal and the tubes werethen heated to between 500 and 600 C. for above five minutes. Thetreated tubes were then filled with shaving cream having a pH of about9.8. No reaction between shaving cream and tube could be discovered andthe tube remained free of corrosion and deterioration after four monthsstorage at 50 C. i

A mustard oil food product having a pH of 3.94 packed in tubes treatedas above was stored for four months at 50 C. At the end of this storageperiod the tubes were opened. The mustard-oil product was unchanged intaste and remained completely usable as a foodstufi. The tubes wereuncorroded and retained their orginal surface characteristics ofbrightness and smoothness.

A series of aluminum panels of 10 mils thickness were dipped in a 10percent by weight solution of m-ethyltrimethoxy silane in benzene. Thepanels were air-dried. The coated panels and some uncoated controlpanels were placed in an air circulating oven and heated to about 500 C.for 30 minutes. The coated panels and control panels were then immersedin concentrated hydrochloric acid for several hours. The coated panelsshowed substantially no attack at the end of the test but the untreatedcontrol panels were gradually and progressively corroded and fell apartbefore the end of the test.

The foregoing are exemplary of the excellent results achieved throughthis invention. Similar results are achieved with copper, nickel andmagnesium similarly coated. When phenyltrimethoxy silane, ethyldimethoxyhydroxy silane and methylhydrogenmethoxy siloxanes of the averageunit formula CH H Si(OMe) O- where a has an average value of 0.25 and bhas an average value of 0.75 are substituted for the silanes employed inthe rforegoing examples, similar corrosion resistance is imparted to themetals.

Corrosion resistance will be considerably increased when conventionalcatalysts are addedwhich facilitate the hydrolysis of alkoxy silanes andaccelerate the condensation of silicon organic compounds.

Substances facilitating hydrolysis include phosphoric acid and ferricchloride. Substances which accelerate condensation are all organometalcompounds which in silicone chemistry areuseful as condensationcatalysts. Such substances include metal salts of carboxylic acids,alcoholates of heavy metals, metal chelates and the like, [for exampletitanic acid esters, and organic Zinc, tin, aluminum, lead, andzirconium compounds such as tetrabutyl titanate, dibutyl tin diacetateand dimaleinate, zirconium acetyl acetonate.

The aluminum surfaces are treated as described above.

Table Amount Treatment of aluminum of H, Time (1) No treatment 1 1'30 21'45 3 1'54" (2) 10% GH3SKOC2H5 3 in isopropyl alcohol 1 4:30;:

2 5 30 3 an" (3) 10% (GH3)iSi(OCzH5)z in isopropyl alcohol. 1 2:20

2 2 40 3 2'50 (4) 10% OH Si(OH) in isopropyl alcohol 1 1047 2 ll 51 31232" (5) 10% CH Sl(OC2H5)3 3% dibutyl tin dilaurate in isopropylalcohol 1 630 2 7'19 3 7'50" (6) 10% ClI3Sl(OC2H5)3 3% zirconium acetylacetonate in isopropyl alcohol 1 7'49 2 823 3 8 47 (7) 10% OH3Si OO2H5 33% phosphoric acid (89%) in isopropyl alcohol 1 1O051 2 1 3 1130 (8)6.6% CI-I3Si(OOQH5) 2.4% (CHs flSi(O 0 11 2 1% butyl titanate inisopropyl alcohol 1 1507 (This solution had been stored 18 months). 21647 3 1737 (9) 10% OH3Si(OH) 3% H3PO4 (89%) 3 2040 (10) 10% (OHS)Zl(OOZH5)Z 3% buty1titanate 3'40 3 4'18 (11) 10% OH3Si(OH)a 3% butyltltanate 1 1218 2 13/55 3 1449 That which is claimed is:

l. The method of imparting corrosion resistance to metallic surfacesselected from the group consisting of aluminum, copper, nickel andmagnesium consisting essentially of coating the surface of the metalwith an organosilicon composition selected from the group consisting ofat least one silane of the formula n m )i n m and siloxanes of the unitformula n m (OR, 4-nm-x x 2 wherein each R is selected from the groupconsisting of monovalent hydrocarbon radicals free of aliphaticunsaturation and halogenated monovalent hydrocarbon radicals free ofaliphatic unsaturation, each R is selected from the group consisting ofhydrogen atom and alkyl radicals, m has an average value of 0 to 1inclusive, n has an average value of .9 to 1.2 inclusive and x has anaverage value of from 1 to 2 inclusive, the sum of n-l-m-l-x being lessthan 4-, and thereafter heating the coated metal to a temperature of 350C. to 600 C. until the organosilicon coating is cured.

2. The method of claim 1 wherein the organosilicon compound is appliedto the metal surface from a solution in an organic solvent.

3. The method of claim 2 wherein aluminum is coated with a mixture ofmethyltrimethoxy silane and phenyltrimethoxy silane.

4. 'lhe method of claim 2 wherein the organosilicon compound ismethyltrimethoxy silane.

5, The method 'of claim} wherein the organosilicon compound ismethyltriethoxy silane.

6. The method of imparting corrosion resistance to metals selected fromthe group consisting of copper, nickel, aluminum, and magnesium,consisting essentially:

of coating the metal with at least one 'monoorganosilicon compoundselected from the group consisting of silanes of the general formula R HSi(OR') wherein each R is selected from the group consisting ofmonovalent hydrocarbon radicals free o f aliphatic unsaturation andhalogenated monovalent hydrocarbon radicals free of aliphaticunsaturation, each R, .is selected from the group consisting of thehydrogen atom and alkyl radicals, m 'has an average value of from 0 to linclusive, n has an average value of [from .9 to 1.2 inclusive, andpartial hydrolyzates of such 'silanes, and heating the metal to therange above 350 C. and below the melting point of the metal until theorganosilicon coating is cured.

compound isapplied to the-metal surface from a solution in an'organicsolvent.

8. Amethod of'impartingfresistance to alkali and, acid 20 7. The methodof claim 6 wherein the or'gan'osilicone to aluminum consistingessentially of coating the aluminum with a monoorganosilan-e of theformula n n mnn where each R is an alkyl radical, each R is an alkylradical and n has an average valueof .9 to 1.2 inclusive and heating thecoated metal to a temperature in the range 350 to 600 C. until thesilarre is cured.

9. The method of claim 8 wherein the organosilicon compound is appliedto the metal surface from a solution in an organic solvent.

'Reierences Cited in the file of this patent- UNITED STATES PATENTS650,131 Great Britain Feb. 14, 1951 Rochow ou. 7, 194,1

1. THE METHOD OF IMPARTING CORROSION RESISTANCE TO METALLIC SURFACESSELECTED FROM THE GROUP CONSISTING OF ALUMINUM, COPPER, NICKEL ANDMAGNESIUM CONSISTING ESSENTIALLY OF COATING THE SURFACE OF THE METALWITH AN ORGANOSILICON COMPOSITION SELECTED FROM THE GROUP CONSISTING OFAT LEAST ONE SILANE OF THE FORMULA